Ppf

Do we have the option of closing the PPF Account if so whether the proceeds are taxable?

Actually i have heard that it is not permissible for us to close the account prior to 15 years lock in period then if withdrawn 50% after seven years then whether it is taxable and what all portion is taxable whether the principal amount or interest amount?

And if at all i have to transfer the same to my NRI Account then what is the procedure.